Short-Term Debt and Credit Agreements (Narrative) (Detail) - USD ($)		1 Months Ended		12 Months Ended
		Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2021	Jul. 31, 2021	Jun. 30, 2021	Dec. 31, 2020	Oct. 31, 2020	Apr. 30, 2020	Dec. 31, 2019	Nov. 30, 2017
Debt Instrument [Line Items]
Facility Limit	[1]			$ 6,000,000,000			$ 6,000,000,000
Short-term debt				2,314,000,000			895,000,000
Letters of credit outstanding, amount	[1]			131,000,000			100,000,000
Floating Rate Demand Notes
Debt Instrument [Line Items]
Short-term debt				431,000,000			268,000,000
Floating Rate Demand Notes | Shelf Registration for Sale of Demand Notes
Debt Instrument [Line Items]
Facility Limit											$ 3,000,000,000.0
Debt instrument, maximum principal outstanding amount								$ 1,000,000,000.0
Dominion Energy South Carolina Inc
Debt Instrument [Line Items]
Facility Limit				500,000,000
Short-term indebtedness outstanding		$ 2,200,000,000
Debt, maturity month and year		2023-03
Questar Gas
Debt Instrument [Line Items]
Facility Limit				250,000,000
GENCO
Debt Instrument [Line Items]
Short-term indebtedness outstanding		$ 200,000,000
Debt, maturity month and year		2023-03
SBL Holdco
Debt Instrument [Line Items]
Facility Limit				30,000,000
Short-term debt							0
Dominion Solar Projects III, Inc
Debt Instrument [Line Items]
Facility Limit				25,000,000
Short-term debt							0
Revolving Credit Facility
Debt Instrument [Line Items]
Facility Limit						$ 6,000,000,000.0
Letter of Credit
Debt Instrument [Line Items]
Facility Limit				$ 2,000,000,000.0
Letter of Credit | Credit Facility, Maturing in June 2022
Debt Instrument [Line Items]
Facility Limit									$ 30,000,000
Credit facility, maturity date				Jun. 30, 2022
Credit facility, amount borrowed							29,000,000			$ 30,000,000
364-Day Revolving Credit Facility
Debt Instrument [Line Items]
Facility Limit			$ 900,000,000
Short-term debt							$ 225,000,000
Debt Instrument Term			364 days
Term Loan Credit Agreement
Debt Instrument [Line Items]
Facility Limit					$ 1,300,000,000
Credit Facilities Maturing in December 2021 with 1 Year Automatic Renewals Through 2024 | DECP Holdings
Debt Instrument [Line Items]
Facility Limit				$ 110,000,000
Automatic renewal period				1 year
Letters of credit outstanding, amount				$ 110,000,000
Letters of credit borrowed, amount				$ 0

[1] This credit facility matures in June 2026, with the potential to be extended by the borrowers to June 2028, and can be used by the borrowers under the credit facility to support bank borrowings and the issuance of commercial paper, as well as to support up to a combined $2.0 billion of letters of credit.